1. Field of the Invention
The invention relates to a wheel assembly with an in-wheel motor, which transmits rotational output of the motor to a wheel via a counter gear.
2. Description of the Related Art
A vehicle having a related wheel assembly with an in-wheel motor that can individually control the braking/driving force of each wheel is known. There are many types of wheel assemblies with in-wheel motors, some of which transmit output from the motor to the wheel via reduction gears, while others transmit output of the motor directly to the wheel using a direct drive method without going through reduction gears. Japanese Patent Application Publication No. JP-A-2004-90822, for example, describes one of the former types, in which an output shaft of the motor is arranged offset in the longitudinal direction with respect to an axle center.
In the foregoing wheel assembly with an in-wheel motor, a pair of bearings are usually installed for the output shaft of the motor and the rotating center shaft of the reduction mechanism. In order to prevent noise, each gear of the reduction mechanism normally has an angle of torsion (i.e., helical gears are normally used instead of spur gears). This angle of torsion, however, generates axial force (i.e., thrust force). Therefore, the bearings that receive this axial force must be supported by members having high strength and rigidity. However, making the portions that support these bearings extremely strong and rigid by increasing their thickness also increases weight and reduces space within the wheels, which is unreasonable.